Due to the exhaustion of traditional energy sources together with an increase in the global energy demand, impetus is currently being given to the development of alternative energy sources. Among them, biomass is a renewable quantitative biological resource that attracts a great deal of attention.
Among biomass-based industrial raw materials, isosorbide (C6H10O4) that is prepared by dehydration of sorbitol (C6H14O6) under acid catalyst conditions attracts attention as an environmentally friendly raw material for preparing polycarbonate (PC) as a substitute for bisphenol A (BPA), an epoxy monomer or an environmentally friendly plasticizer.
A reaction that converts sorbitol to isosorbide is a dehydration reaction that removes two water molecules from sorbitol in the presence of an acid catalyst. During dehydration of sorbitol molecules, oligomers and polymers can be produced by polymerization of a reaction intermediate, side-reaction products or isosorbide, and such polymers are carbonized during an additional dehydration process at high temperature to form carbonized materials. The carbonized materials reduce fluidity in the dehydration reactor while becoming solid. Finally, the carbonized materials become a solid having no fluidity, interfere with the flow of fluids in the reactor and pipelines, and also interfere with stirrer operation.
Among compounds formed by side reactions, a dihydrofuran compound is expected to be a major compound that is likely to cause polymerization. To prevent dehydration polymerization from being caused by the dihydrofuran compound, compounds having an alcohol group and compounds having an amide or thiol group, which may have an action similar to that of the alcohol group-containing compounds, are contemplated as additives that bond with the dihydrofuran compound to terminate the reaction.
Korean Patent Publication No. 2014-0048439 discloses a method for producing anhydrosugar alcohol, which comprises a step of converting hydrogenated sugar to anhydrosugar alcohol by a dehydration reaction and which is carried out in the presence of a polyol, such as ethylene glycol, polyethylene glycol, polypropylene glycol, glycerol or the like, as a reaction diluent in the dehydration reaction. However, because a reaction for producing isosorbide is generally carried out at high temperature under a vacuum, a high-boiling-point compound which is not volatilized under the reaction conditions should be added during the reaction. In addition, if the compound added has several functional groups such as alcohol groups, there will be a problem in that additional dehydration reactions in addition to the production of a reaction intermediate occur depending on reaction conditions, and for this reason, the yield of anhydrosugar alcohol is reduced.
Accordingly, the present inventors have found that, when a high-boiling-point compound, which is not volatilized under reaction conditions and has one alcohol group, is added during dehydration of sorbitol molecules in order to solve the problems that carbonized materials derived from oligomers or polymers, produced by polymerization of a reaction intermediate, side-reaction products or isosorbide during the dehydration, reduce fluidity in the dehydration reactor while becoming solid, interfere with the flow of fluids in the reactor and pipelines and also interfere with stirrer operation, it can inhibit the polymerization during dehydration to inhibit the production of the carbonized materials, thereby completing the present invention.